No abstract available

No abstract available

[en] The seismic response of a great pebble bed HTR has been examined theoretically by preliminary calculations. The total system to be considered, consisting of the core and the side reflector, is restrained by spring pack assemblies. The calculations of the natural frequency of the pebble bed based on different theoretical models led to values of 6 to 10 Hz or higher. This is close beyond the region of maximum magnification. The natural frequency of the system side reflector-pebble bed was found to be approx. 10 Hz or more, which assures rigid body behavior. The seismic behavior of the KLAK shut down system has been investigated experimentally. Most of the KLAKs will remain inside the pebble bed during an earthquake, they will be removed totally only from a flat layer of the pebble bed surface. To get more exact information about the pebble bed reactor seismic response the calculations shall be checked by model experiments with different scaled-down HTGR-core models. The main concerns of these investigations are: dynamic behavior of the pebble bed; sloshing of pebbles at the core surface and at higher acceleration levels possibly inside the core; dynamic response of the side reflector and its interaction with pebble bed and spring packs; collisions between the blocks within the top reflector and between the outer blocks of the top reflector and the side reflector; and adaption of the parameters to different computer codes to calculate the dynamic behavior of the reactor more precisely

No abstract available

[en] The two-dimensional cylindrical model of HTR-ASTRA fuel pebble bed assembly was used in the transport calculations of k_eff and corresponding Rossi-α for interpretation of pulsed neutron measurements which have been carrying out during approach to critical mass. This analysis demonstrates possibility to evaluate k_eff above 0.9 using α-prompt decay constant measured during core loading by fuel balls and to extrapolate these data for determination of critical mass similar to inverse counting technique

[en] The loading of the inside of the reactor with fuel element pellets is done via a central tube. There is a blower in the area of the tube, by which the compressed air and the suction air in the tube can be varied. In this way, the speed of fall of the fuel element pellets in the tube is variable, so that they hit the pebble bed with different speeds of fall. The place at which the fuel element comes to rest on the heap inside the reactor can be determined in this way, within certain limits. (DG)

[en] The device makes it possible to achieve an even design of the edge zone with a small number of supply pipes, without adverse effect on the flow of pellet operating elements into the active core. In order to build up the edge zone, an annular separation reaching to the surface of the pebble bed is fitted to the lower edge of the ceiling reflector, so that an annular gap is formed between the solid reflector jacket and the pebble bed separation, in which the graphite elements of the edge zone are placed and which is continued to the ceiling reflector. The central surface of the edge zone lies above the central surface of the operating pebble bed, preferably inside the part of the annular gap situated in the ceiling reflector. (orig./HP)

[en] Nuclear fuel cycles were evaluated for the Pebble Bed Gas Cooled Reactor under development in the Federal Republic of Germany. The basic fuel cycle specified for the HTR-K and PNP is well qualified and will meet the requirements of these reactors. Twenty alternate fuel cycles are described, including high-conversion cycles, net-breeding cycles, and proliferation-resistant cycles. High-conversion cycles, which have a high probability of being successfully developed, promise a significant improvement in resource utilization. Proliferation-resistant cycles, also with a high probability of successful development, conpare very favorably with those for other types of reactors. Most of the advanced cycles could be adapted to first-generation pebble bed reactors with no significant modifications

[en] In order to increase safety, particularly for the reliable removal of post-fission heat, for example in accidents, a heat exchanger is accommodated in the side reflector, which is connected to a hot and cold water pipe, which in turn forms the secondary circuit. (DG)

[en] If a graphite reflector of a pebble bed reactor is equipped with insertable absorber rods power control is achieved by less insertion depth of these rods than would be required for conventional designs for the same type of reactor. Therefore the difficulties growing with insertion depth and the danger of damaging fuel elements are reduced. With less stroke, the drives of the control rods are simplified, too. A means for this is doping the graphitic reflector bottom and the lower part of the reflector with neutron-absorbing material. A partial flow of neutrons forced downwards on insertion of the control rods into the upper zone of the reflector will be absorbed in this lower region. A formula is given for this doping. (HP)